1-url image 转为file

var img =
  "https://ss0.bdstatic.com/70cFuHSh_Q1YnxGkpoWK1HF6hhy/it/u=508387608,2848974022&fm=26&gp=0.jpg"; //imgurl 就是你的图片路径
function getBase64Image(img) {
  var canvas = document.createElement("canvas");
  canvas.width = img.width;
  canvas.height = img.height;
  var ctx = canvas.getContext("2d");
  ctx.drawImage(img, 0, 0, img.width, img.height);
  var ext = img.src.substring(img.src.lastIndexOf(".") + 1).toLowerCase();
  var dataURL = canvas.toDataURL("image/" + ext);
  return dataURL;
}
var image = new Image();
image.src = img;
image.setAttribute("crossOrigin", "Anonymous");
image.onload = function() {
  var base64 = getBase64Image(image);
  console.log(base64);
  document.getElementById("img").src = base64;
  var formData = new FormData(); 
  //转换base64到file
  var file = btof(base64, "test");
  formData.append("imageName", file);
};
function btof(data, fileName) {
  const dataArr = data.split(",");
  const byteString = atob(dataArr[1]);
  const options = {
    type: "image/jpeg",
    endings: "native"
  };
  const u8Arr = new Uint8Array(byteString.length);
  for (let i = 0; i < byteString.length; i++) {
    u8Arr[i] = byteString.charCodeAt(i);
  }
  return new File([u8Arr], fileName + ".jpg", options);
}